In such a reciprocating pump (German Patent Application DE 35 22 479 A1), a plurality of pistons arranged in a star configuration are driven by means of an eccentric provided on a drive shaft. A bush that is nonrotatable in the pump housing is supported as a stroke ring on the eccentric and on its outer circumferential face has one bearing face for each piston, on which face a slide cushion rests. On this slide cushion, the piston is supported with a steel disk mounted on its corresponding end.
In this known pump, the delivery and withdrawal of the medium to be pumped to and from the work chamber are effected through the same line, using control valves; the piston is held in contact with the stroke ring by the delivered medium to be pumped.
In this reciprocating pump, instead of the steel disk it is also possible for a tappet to be inserted into a recess in the piston that is open toward the stroke ring. The tappet then rests with a flange on the slide cushion and is pressed against the stroke ring by a compression spring disposed in the tappet interior. The tappet thus remains in contact with the stroke ring even if the delivery of medium to be pumped is interrupted, and thus prevents an undesired rotation of the stroke ring relative to the housing.
To attain a shock absorbing effect, the tappet is provided with a supply connection and an axial bore, through which oil can be delivered to the interior of the tappet and piston.
"Hydraulik in Theorie und Praxis. von Bosch." [Hydraulics in Theory and Practice, by Bosch], by W. Gotz, 1983, published by Robert Bosch GmbH, Stuttgart, discloses a radial reciprocating pump with external piston support, in which a cylinder star is driven by a drive shaft. The cylinder star has a plurality of cylinders in which radially displaceable pistons are disposed, and the pistons are supported radially on the outside via sliding blocks on the inside circumference of a stroke ring that is disposed essentially in a manner fixed against relative rotation and eccentrically to the cylinder star in the leakage chamber of the pump. The pistons are held in contact with the stroke ring by the medium to be pumped.
In order to achieve a hydrostatic bearing relief of the slide bearings formed by the stroke ring and the sliding blocks, each sliding block, in the middle of its slide face, has a recess that communicates with the respective cylinder chamber. In operation of this known pump, the sliding blocks always move in the same direction along the inside circumferential surface of the stroke ring.
"Bosch-Hydraulik: Informationen und Daten 1970/71" [Bosch Hydraulics, Information and Data, 1970-71], p. 57, an axial reciprocating pump of the oblique disk type is known, in which the axial pistons are disposed in corresponding bores of a pump body that is driven by a drive shaft. The pistons are supported via sliding blocks on the working face of an oblique disk provided in the leakage chamber of the pump, and the sliding blocks are held in contact with the oblique disk by a holding-down ring.
To achieve hydrostatic bearing relief of the slide bearings formed by the oblique disk and the sliding blocks, a recess in the middle of the slide face of the sliding blocks communicates with the respective work chamber. In this known pump as well, during operation the sliding blocks always move in the same direction along the working surface of the oblique disk.
Another known radial reciprocating pump (German Patent DE 37 26 957 C2) has pistons, which are guided in cylinders disposed on the housing. The pistons are driven by a drive shaft via an eccentric. For supporting the pistons on the jacket face of the eccentrics, a sliding block is mounted on the piston, and a recess is provided in its support face that rests on the jacket face of the eccentric; the recess communicates with the respective associated work chamber, for the sake of hydrostatic bearing relief. The effective area of the recess serving the purpose of bearing relief is less than the effective piston area. In this known pump as well, the sliding blocks always move in the same direction relative to the support bearing face on the eccentric.